In communication networks in which the Common Channel Signaling System 7 CCS7, also referred to as SS7, standardized by the International Telecommunication Union ITU, is used in accordance with ITU-T recommendations Q.700 and later for the transmission of messages, communication between two signaling points SP, i.e. nodes and/or end points of the communication network, via connections, which in this context are referred to as signaling links or SS7 links. A node is also referred to as a signaling transfer point STP, while an end point is also referred to as a signaling end point SEP.
As disclosed in ITU-T Q.700ff, it is possible in SS7 communication networks to combine signaling links in what are known as signaling link sets. Each signaling link set comprises at least one signaling link but a maximum of 16 signaling links.
The architecture of the SS7 is also disclosed in ITU-T Q.700ff. A distinction is made between different protocol levels. Levels 1–3 form the message transfer part MTP. A number of level 4 protocols are defined in the SS7 and are referred to here as user parts UP. Examples of such are the telephone user part IUP, the ISDN user part ISUP or the signaling connection control part SCCP. Messages from these user parts are transmitted securely by the MTP.
In known SS7 implementations until now messages have been routed not in a source-related manner but purely in a destination-related manner. However it can be advantageous to route messages to one destination from different sources via different routes. This could for example be done to avoid specific message routes or to comply with business or security-related agreements. A further case for applying source-based message routing occurs when a number of link sets are provided between two nodes, for example between a signaling transfer point STP and a home location register HLR, due to a high level of expected load.
A number of link sets can be provided between two signaling points to increase the maximum number of links and therefore the transmission capacity between these two signaling points (a link set can have a maximum of 16 links). In such a case the traffic from the STP to the HLR is to be distributed to the individual link sets in a source-based manner in order to distribute the load. A further problem can then arise if the link sets, of which there are more than one, between the signaling points are implemented according to the standard. As, according to the ITU standard, only one link set can be provided in an MTP network between two signaling points, the link sets, of which there are more than one, must in this case be associated in at least one of the signaling points, advantageously in the STP, with different logical message transfer part MTP networks. The further problem then arises of how a message, which was received in one network, can be forwarded via a link set in a different network.
Similarly messages can only be forwarded by the MTP in an STP in the network in which they were received. The following techniques are also known:
Screening functions, for example according to ITU-T Q.705, allow differentiation so that for example messages from a specific source or from a specific link set may not be routed to specific destinations. This function can be linked to a charge function. Both sources and link sets as well as destinations can then be combined in groups, which are processed in the same way. This method however only allows a yes/no decision and usually all messages (except for the outgoing link set/DPC screening removed from Q.705 due to problems with route planning), which are subject to the screening function, are each routed to one destination in an identical manner.
A further known method involves not allowing or only to some extent allowing alternative routes to specific destinations for traffic not originating in the particular node, known as foreign traffic. The procedure here is such that, if a higher priority alternative route to a destination is not authorized for foreign traffic, lower priority routes to the same destination are not authorized either. This results in the significant restriction that higher or highest priority routes are used regardless of source, and route priority, if permitted, is identical.
A method is also disclosed in EP 1 130 930, with which link sets are divided into groups and with which the routes to a destination permitted for a message depend on the association of the source, i.e. the link sets, at which the message was received, with a group. This also results in the restriction that higher or highest priority routes are used regardless of source, and route priority, if permitted, is identical.
A check is also known, which ensures that messages from one link set are not forwarded again via the same link set (avoiding what are known as ping-pong loops). However this only serves to prevent errors, not to route in a source-based manner. WO99/55098 and WO00/11883 also disclose how messages can cross MTP network boundaries in a node via physical or virtual tunnels. They also disclose how certain screening functions can be achieved with these methods. However they do as little to achieve a solution to source-based routing as the screening functions. The problem of crossing network boundaries is however resolved. However the two solutions have the following disadvantages:                All the messages arriving in a network are forwarded via the same networks or the same other network, so source-based routing can only be achieved to a very limited extent.        The physical tunnels according to WO99/55098 also have the disadvantage that they use physical resources, by connecting two logical networks via one physical link set. In addition to the disadvantageous use of resources, the traffic between the two networks is also restricted with regard to volume as a result.        The virtual tunnels also have the disadvantage that setting them up fully according to standards—particularly for MTP network management—can be very expensive for existing implementations.        
It is also possible to define routing tables based on source or based on the link set of incoming messages. This method is the most flexible but it requires a great deal of storage capacity for the routing tables and very complex and time-consuming network management, partly because a large number of routing tables have to be changed after events which require routing table changes. The implementation of such a function, particularly in existing systems, is also expensive and complicated. Nor does it result in the crossing of network boundaries.
Finally a development of the above method is known, which, unlike the ITU standard, provides a number of logical addresses in a node in a logical network, said addresses being known here as signaling point codes SPC, from each of which separate link sets can lead to a specific adjacent node and in which incoming messages can be routes in a source-based manner. This method may resolve all the problems listed but it is extremely uneconomical with regard to use of resources and set-up costs. This is particularly true of existing systems.